Sandwich base structure for off-shore wind turbines

ABSTRACT

The invention relates to a base structure ( 1 ) for an off-shore wind power installation having at least a plurality of, in particular three, bases piles ( 2, 3,, 4 ), and a support structure ( 5 ) connecting the upper ends of the base piles ( 2, 3, 4 ) for the pylon of the wind power installation. Furthermore each base pile ( 2, 3, 4 ) has a wall comprising a plurality of layers ( 19, 20, 21 ) of differing material substantially over its entire length, wherein the wall is formed from at least one surface portion, having an inner layer ( 19 ) and an outer layer ( 20 ) and wherein a core material is arranged between the inner layer ( 19 ) and the outer layer ( 20 ) as an intermediate layer ( 21 ).

The invention relates to a base structure for an off-shore wind power installation having at least a plurality of base foundation piles, wherein each base pile has a driving pile which is guided in its interior at least portion-wise for anchoring in the seabed, and at least one support structure for mounting the hydraulic structure, wherein the support structure connects the upper ends of the base piles together.

The invention further also concerns a base structure for an off-shore wind power installation having at least a plurality of base foundation piles, and at least one support structure connecting the upper ends of the base piles for the pylon of the wind power installation.

Base structures of the above-indicated kind, in particular base structures for off-shore wind power installations, are used predominantly to be able to set up wind power installations in so-called off-shore wind parks. So that the installation can be set up at a sufficient distance from the coast it is generally necessary to anchor the wind power installations in depths of water of between 20 and 50 meters by means of the base structures. That is always intended to ensure operationally reliable long-term function of the base structures used for at least 20 years.

By virtue of the ambient conditions prevailing at such an installation location and the wind and wave loads which generally act on the base structure and the hydraulic structure, correspondingly high demands are made on anchorage of the base structure in the seabed and the base structure carrying the hydraulic structure itself.

The steady increase in the electric powers generated by the wind power installations to be assembled, of at the present time 5 MW, means that the demands on the strength of the base structures carrying the wind power installations are also rising. In addition the demands rise further, the greater the depths of water in which the wind power installations are set up in the form of wind parks. To ensure adequate strength for the base structure and thus to avoid in particular permanent deformation both the base piles and also the support structure are of corresponding wall thicknesses of steel of for example between 50 and 70 millimeters. In that respect such wall thicknesses are necessary to avoid buckling of the steel which is predominantly used. The relatively large wall thicknesses however involve on the one hand high production and material costs while on the other hand such base structures are of relatively high inherent weight so that such base structures can usually only be moved or managed with the heaviest lifting equipment.

EP 1 673 536 B1 describes for example a base structure for an off-shore wind power installation, having a plurality of base piles with respective driving piles which are at least portion-wise guided in the interior of the respective base piles, for anchorage in the seabed. The base structure further has at least one support structure for mounting the pylon of the wind power installation, wherein the support structure connects the upper ends of the base piles together. In that case, after piling of the driving piles, a predetermined lengthwise portion is produced, in which the driving piles are received by the base piles. To prevent relative movement between the base piles and the driving piles and thereby possibly cause loosening of the anchorage of the base structure in the seabed, an adhesive join is made in a part of the overlap region between the outside of the driving pile and the inside of the base pile. The relatively narrow adhesive join between the outside of the base pile and the inside of the driving pile means that on the one hand there is the risk that the adhesive tears and thus the driving pile is again movable relative to the base pile. In addition, it is in the region of the seabed that the highest moment caused by the wind and wave loads acts on the base and driving piles of the base structure so that the constant changes in load shortly beneath the overlap region of the piles can result in deformation and possibly bending of the walls of the driving piles, which at any event can have a detrimental effect on the anchorage thereof and thus on the operationally reliable long-term function of the base structure.

Therefore the object of the present invention is to improve a base structure of the above-indicated kind such that deformations at the piles due to the changing loads acting thereon are avoided.

A further object of the invention is to improve a base structure of the above-indicated kind such that production thereof is possible in a simplified fashion and thus inexpensively while on the other hand transport to the installation location can be effected at a reduced level of complication and expenditure.

According to the invention the object is attained by a base structure having the features of claim 1. Advantageous developments and configurations of the invention are recited in the appendant claims.

In the case of a base structure for an off-shore wind power installation having at least a plurality of base piles, wherein each base pile has a driving pile guided in its interior at least in portion-wise manner for anchorage in the seabed, and at least one support structure for mounting the pylon of a wind power installation, wherein the support structure connects the upper ends of the base piles together, it is provided that the base pile and the driving pile have a region of overlap on a predetermined lengthwise portion, wherein in the overlap region of the piles, in at least portion-wise manner, the gap between the piles, and over a portion of the overlap region and in a part beneath the overlap region, the free internal cross-section of the driving pile is filled with a hardening filling material.

By means of such a strong structure around the overlap region of the base piles and the driving piles which are region-wise accommodated by the base piles, in particular buckling or kinking of the pile walls is advantageously prevented in the region of the seabed by the filling material which has portion-wise hardened within the driving pile and between the base pile and the driving pile. The filling material which extends to beneath the overlap region in the interior of the driving pile imparts thereto optimum stiffness over a predetermined part thereof, whereby the driving pile can be made up from a single-walled tube. The hardening filling material which preferably respectively extends from below to above the overlap region, such as for example concrete, advantageously produces a base structure, by means of which it is possible without any problem to guarantee an operationally reliable long-term function of the at least required period of 20 years.

It is advantageously provided in a development that the base pile in the foot region has a guide for the driving pile, which reduces the free cross-section of the base pile at the inner peripheral surface. The use of a guide has the advantage that the driving pile is axially movably guided during the driving operation in particular at the beginning of the driving works, so that the driving pile is driven into the seabed with its center line preferably coaxially with respect to the center line of the base pile. That is intended advantageously to prevent the driving pile from running out. In that case the guide is provided approximately over half of the overlap region of the two piles in the gap between the inside of the base pile and the outside of the driving pile at least region-wise over the periphery thereof. The guide can be for example in the form of a sleeve. Preferably a plurality of plates are used, the longitudinal axes of which extend parallel to the center line of the base pile and extend radially from the inside of the base pile in the direction of the center line.

Optionally the base pile has a bottom ring with a seal which seals off the gap relative to the driving pile, whereby on the one hand the ingress of sea water, as well as pieces of rock and mud, in particular into the gap in the region of the guide, is avoided during and after the pile driving operation. That therefore prevents unwanted fouling of the portion of the base pile and the driving pile, that is to be subsequently concrete-filled. On the other hand the seal in the region of the gap also prevents the escape of the subsequently introduced filling material. Therefore the hardening filling material always remains at the same level in the gap between the base pile and the driving pile and can accordingly involve a fixed connection to the surfaces of the respective pile walls. To produce the seal on the bottom ring, it is possible for example to use a felt or another suitable material which is suitable for preventing the ingress of water or the entry of mud. In addition, a bursting disk can also be fitted on the bottom ring from below, which disk effectively closes the free cross-section of the driving pile which is preferably in the form of a tube and which is thus downwardly open, and thus already prevents the entry of sea water when lowering the construction part serving to produce the base structure, on to the seabed; the bursting disk is already destroyed by the driving pile which is preferably driven perpendicularly downwardly, when the construction part is placed on the seabed but at the latest with the beginning of the pile driving operation, and in that case the bursting disk does not represent any impediment for the pile driving operations to be performed.

Alternatively it may be advantageous not to provide a seal. Thus when the base structure is lowered from a ship on to the seabed water can pass controlledly and uniformly into the base piles. The risk of a suddenly occurring leak in a sealed base pile causing a sudden shift in the center of gravity and thus tipping of the base structure is reduced. The seal and the bursting disk can then be omitted.

According to the invention the base pile has an inner tube providing its inner peripheral surface and an outer tube providing its outer peripheral surface, a core material being arranged between the inner tube and the outer tube. Such a wall structure according to the invention provides a structurally advantageous possible way of forming the base piles. The sandwich structure of the pile wall on the one hand improves the stiffness of the base pile while on the other hand the amount of steel usually employed to produce the base pile can advantageously be reduced thereby. Due to the increased stiffness, both the diameter and also the overall thickness of the inner and outer tubes can be markedly minimised, which at the same time advantageously improves the economy of such base structures according to the invention by virtue of reduced production and material costs. The core material as the intermediate layer between the inner and outer tubes is in particular additionally strengthened with reinforcement which is arranged in the form of concrete reinforcing steel bars or in the form of a hollow-cylindrical lattice in the core material. It is provided in that case that the reinforcement is always completely enclosed by the core material and is arranged at a spacing relative to the inside of the outer tube and the outside of the inner tube.

According to the invention, in a base structure for an off-shore wind power installation having at least a plurality of base piles and at least one support structure connecting the upper ends of the base piles for the pylon of the wind power installation it is provided that at least a portion of the base structure has a wall comprising a plurality of layers of differing material, wherein the wall is formed from at least one surface portion having an inner layer and an outer layer, and wherein the core material is arranged as an intermediate layer between the inner and outer layers.

The amount of steel required for production of the base structure can advantageously be reduced by means of such a configuration according to the invention in respect of a wall used for producing subregions of the base structure. Both the inner layer and also the outer layer of the wall in that arrangement are of a smaller overall thickness than the wall thicknesses which are otherwise usually required to provide the known base structures. Specifically due to the intermediate layer between the inner layer and the outer layer in the form of a core material which in particular comprises a compression-resistant building material, it is advantageously also possible to increase the strength or stiffness of the wall in spite of the markedly reduced amount of steel. In that case the overall wall thickness of the wall according to the invention of the subregion of the base structure due to the use of the core material between the inner and outer layers, which is preferably made from a steel reinforced material, can be greater than the wall thickness of conventional base structures. In spite of a greater overall wall thickness, the base structure according to the invention, in comparison with a conventional base structure, can be of a lesser inherent weight and can thus be more easily transported to its installation location.

Preferably the wall thickness of the outer and/or inner layer is in a range of between 12 mm and 20 mm, in particular in a range of between 14 mm and 18 mm, and particularly preferably the wall thickness is 16 mm. In that respect the thickness of the core material is preferably in a range of between 60 mm and 120 mm, particularly in a range of between 70 mm and 100 mm, while particularly preferably the thickness of the core material is about 85 mm.

It is advantageously provided in a development of the invention that the inner layer is in the form of an inner tube and the outer layer is in the form of an outer tube extending at a spacing relative to the inner tube. The use of an inner tube and an outer tube, between which the core material is introduced preferably completely or over the full periphery, represents a structurally advantageous possible option for the design configuration of given component regions of the base structure. The cylindrical configuration which is preferred in that respect permits advantageously uniform load application and load distribution over the entire structure of the in particular tubular components of the base structure, which in turn has an advantageous effect on the operationally reliable long-term function of the base structure. In that case the core material is preferably joined over the full surface area involved to the outside of the inner tube and the inside of the outer tube. There is for example a positively locking connection between the core material and the inner and outer tubes respectively. The core material can involve for example a material which can be subsequently introduced between the inner and outer tubes and which gradually hardens and thus imparts a relatively high stiffness to the components of the base structure, that are equipped with that material.

The core material introduced between the inner and outer layers is preferably concrete, the use of which represents an advantageous possible way of producing the compression-resistant core material. Besides its advantageous properties in regard to strength, in particular compression strength, there is the possible option of directly influencing its strength by the change in the composition of the starting materials and thus ensuring optimum adaptation of its physical properties to the respective situation of use. The preferred encapsulation between the inner and outer layers of the wall also provides an advantageous resistance to ageing for the concrete. Buckling or bending of such components of the base structure with a wall according to the invention is advantageously avoided,

The core material is in particular strengthened with reinforcement, whereby the tensile strength of the core material and thus the load-bearing capability of the components of the base structure is improved. The forces which are generated in particular by waves or wind loads and which often act dynamically on the base structure can thus be absorbed without any problem without any detrimental influences on the component structure of the base structure. The reinforcement used is for example concrete reinforcing steel in the form of bars which are distributed for example in a predetermined number uniformly over a predetermined part-circle diameter between the inner and outer tubes. The reinforcement in the form of concrete reinforcing steel bars extends in that case parallel to the center line of the in particular coaxially arranged inner and outer tubes.

One of the partial regions of the base structure is in the form of at least one portion of at least one base pile, representing an advantageously structural configuration of a supporting component of the base structure. Such a configuration according to the invention for the base piles which on the one hand carry the load of the wind power installation and on the other hand ensure a secure connection or anchoring to the seabed provides improved strength or stiffness even in the event of dynamic loadings on the base structure for the off-shore wind power installation. The sandwich structure according to the invention of the wall of the base piles also has an advantageous influence on the operationally reliable long-term function of the overall base structure. Preferably only a predetermined portion of each base pile is of the sandwich structure, extending approximately from the level of the seabed to the upper or free end of the base piles.

It is advantageously provided in a development that the driving pile has a bulkhead which is arranged at a spacing beneath the overlap region and which closes off the free internal cross-section of the driving pile. The entry of water or mud by way of the driving pile which is of a hollow-cylindrical configuration into the interior of the base pile is avoided by means of such a bulkhead in the operation of driving the driving pile so that the free cross-section of the driving pile is filled with seabed only as far as the bulkhead. In addition the bulkhead serves as a filling limit for the filling material which is to be introduced into the driving pile head and which hardens therein and which imparts improved stiffness to the driving pile. The bulkhead is in particular a plate body which extends with its plate plane perpendicularly to the center line of the driving pile and which is sealingly connected in peripheral relationship to the inside of the wall of the driving pile, in particular being welded thereto. In that case the bulkhead is arranged approximately at a spacing beneath the end of the base pile, that corresponds to the length of the overlap of the piles.

To avoid an excessive build-up of pressure in the interior of the driving pile and thus an unnecessary counteracting force in the pile driving operation venting of air from the interior of the driving pile is to be provided. For that purpose in its pile wall beneath the bulkhead the driving pile has at least one opening. Accordingly air in the driving pile can escape in the driving operation so that the constituents of the seabed can rise up in the free cross-section of the driving pile to below the bulkhead. In that respect it is advantageous if a plurality of openings are provided beneath the bulkhead over the length of the driving pile and at the same time a plurality of openings are arranged in the pile wall at the same height level distributed around the periphery of the driving pile. In addition each opening for air venting in the wall of the driving pile can be sealed with a suitable material which dissolves for example upon contact with water and thus the openings are successively opened for air venting purposes in the longitudinal direction in the wall of the pile.

In an optional configuration, at its outside peripheral surface, the driving pile has a radially outwardly extending step as an abutment against the guide of the base pile, by means of which the driving pile is brought into contact in positively locking relationship in the longitudinal direction with in particular the plates forming the guide at the inside of the base pile and exerts a holding force perpendicularly downwardly on the base pile. The step which extends in an annular shape along the peripheral surface of the driving pile is in particular arranged in spaced relationship with the upper end of the driving pile so that there is always a given portion of the driving pile that projects freely into the base pile above the guide. That provides a gap between the outside of the driving pile and the inside of the base pile, into which gap the filling material can be introduced. The radially outwardly extending peripheral surface of the step can be at the same time in the form of a guide surface for support against the inside of the base pile. That further improves guidance for the driving pile within the base pile and at the same time advantageously prevents the driving pile from running out in the pile driving operation. The step can be in particular a flange-like ring body welded to the outer peripheral surface of the driving pile.

Another development provides that the driving pile is at least portion-wise provided with reinforcement on the inside of the pile wall. In particular the subsequently introduced filling material is strengthened by means of the reinforcement, while in addition its tensile strength is increased and thus the load-bearing capability of the piles is markedly improved in the region of the seabed. Specifically forces acting dynamically on the base structure can be absorbed without any problem by the reinforced component structure of the base. In particular concrete reinforcing steel in the form of bars is used as reinforcement, which are arranged on a predetermined part-circle diameter in spaced relationship with the inside of the driving pile. In place of individual bars it is also possible to use a cylindrical reinforcing cage which extends similarly to a mesh on a uniform radius around the center line of the driving pile.

A development of the invention provides that beside the base piles at least one further partial region is in the form of at least one tube portion of a bar of the lattice-like support structure which is composed of a plurality of bars. That advantageously also achieves increased strength in the lattice-like support structure which connects the upper ends together and by means of which the wind power installation is mounted and a direct connection is made between the base structure and the pylon of the wind power installation. The number of bars can be reduced, by virtue of the improved stiffness, by means of the configuration according to the invention of tube portions of the bars used in the support structure. A saving of steel material is advantageously also achieved thereby, in the region of the support structure, with at the same time improved stiffness thereof. The bars used for forming the lattice-like support structure are in particular of a cylindrical cross-section, wherein the configuration of the wall according to the invention can extend both over the entire length of a bar and also only over a given bar or tube portion.

Preferably the wall thickness of the outer and/or inner tube of the bars is in a range of between 12 mm and 30 mm, in particular in a range of between 14 mm and 25 mm, particularly preferably the wall thickness being 16 mm, 20 mm or 25 mm. In that respect the thickness of the core material is preferably in a range of between 60 mm and 120 mm, particularly in a range of between 70 mm and 100 mm, particularly preferably the thickness of the core material being about 85 mm. It will be appreciated that the inner tube and the outer tube may be of varying wall thicknesses.

At at least one of its end regions preferably each tube portion is provided with a bulkhead which sealingly closes off at least its internal free cross-section. That already prevents in particular the ingress of moisture into the interior of the free tube portion before assembly to constitute a support structure connecting the base piles together. Furthermore the bulkhead can additionally serve as a filling limit for a filling material introduced in the region of the node points produced in the support structure. In this connection the bulkhead can be a circular plate body which can be connected at its periphery to the inside of the inner tube, in a connection involving intimate joining of the materials involved, for example by welding.

It is further provided that each tube portion has a reinforcement projecting at its end beyond its bulkhead. The reinforcing steel which is used for example between the outer and inner tubes of the tube portion accordingly projects beyond the bulkhead into a filling space for filling material to be introduced thereinto, the filling space possibly being formed on both sides of the ends of the tube portion of the bar of the support structure. When using a hardening filling material the projecting portions of the reinforcement of the tube portion then involve a connection to the hardened filling material, that involves intimate joining of the materials involved, after the filling material has set.

At at least one of its ends each tube portion has an annular connecting surface extending in a plane oriented perpendicularly to the center line of the tube portion. A respective tube portion involving the sandwich structure according to the invention accordingly always has straight ends extending perpendicularly to its center line. Each tube portion according to the invention can be connected to connecting tube portions forming the ends of a respective bar, by way of the straight ends having a respecting connecting surface at the ends. The connection of a respective individually prefabricated tube portion to a connecting tube portion of conventional nature can in that case be advantageously easily effected by means of orbital welding devices, wherein the tube portion and the connecting tube portion are in particular welded together to form a bar of the support structure.

In an alternative or additionally thereto arranged at at least one and preferably two axial ends of a base pile and/or a bar is a sandwich connection which connects the inner and outer layers together and which in the axial direction forms a prolongation of the base pile and/or the bar in the form of a connecting tube. Preferably the sandwich connection is welded to the tubes forming the inner and outer layers. This on the one hand ensures a stable connection between the tubes forming the inner and outer layers and the ring flange while on the other hand the intermediate layer is completely enclosed and thus protected from weather. In addition reinforcements between the inner and outer layers can be fixed to the sandwich connection. Such a reinforcement can comprise for example steel bars extending parallel to a longitudinal axis of the tubes therebetween. The steel bars are then preferably fixed to two sandwich connections arranged at the opposite ends of the tubes, in particular being welded or screwed thereto. In that way a tensile force can be better transmitted by means of the bar in the form of a sandwich tube. In particular concrete which is introduced as the intermediate layer is suitable for the transmission of compression forces but less suitable for the transmission of tensile forces. Higher tensile forces can be transmitted by fixing reinforcing bars between the sandwich connections arranged at the opposite ends of the bars.

The sandwich connection forms an axial prolongation of the base pile and/or the bar. That prolongation preferably corresponds to the shape of a connecting tube. The diameter of the connecting tube preferably corresponds to the mean diameter of the tube portion in the form of the sandwich tube. By means of such a connecting tube, the base piles and/or the bars can advantageously be connected to further bars to afford a support structure or the base piles can be connected to the support structure. Such a connection is particularly simple to make by means of orbital welding. For that purpose for example two connecting tubes can be fitted together in butting relationship and the connection can be made by means of orbital welding. In that way a base structure having for example base piles and a support structure in the form of a jacket structure can be composed of individual sandwich tubes, wherein the individual sandwich tubes can be connected together by means of the connecting tubes in conventional fashion. Known problems which can occur when joining sandwich tubes are avoided in that way. In particular the individual connections or weld points between two tubes can be easily calculated.

Preferably the sandwich connection has a ring flange which is substantially conical in cross-section, wherein the ring flange is connected at one end to the inner layer and the outer layer and at the other end to a connecting tube. Such a ring flange can be produced for example by means of rolling. This is a widespread production process whereby costs for a base structure are reduced. At its wider end the ring flange is preferably of a thickness substantially corresponding to that of the sandwich portion of the tube or of the bar. The thickness preferably approximately corresponds to the difference between the outside diameter of the outer tube and the inside diameter of the inner tube. The narrower end of the ring flange can be connected to a solid massive connecting tube. The solid massive connecting tube is preferably of a diameter corresponding to the mean diameter of the sandwich tube. The thickness of the connecting tube is to be selected according to the loading involved. The thickness of the narrower end of the ring flange is adapted to the thickness of the connecting tube.

It is further preferable for the ring flange to have openings for receiving reinforcing bars. Preferably the openings are in the form of through holes. The openings are preferably arranged uniformly around a periphery of the ring flange. The openings are of such a diameter that reinforcing bars can be passed therethrough. Preferably the reinforcing bars are welded to the ring flange.

In a preferred embodiment in the base structure it has at least one connecting body having two or more connecting tubes for connection, in particular welding, to connecting tubes or sandwich connections of a respective base pile and at least one bar of the support structure. The bars of the support structure are generally not fixed to the base piles coaxially with respect thereto but are at predetermined angles. Thus a support structure frequently has so-called transverse locking bars which are oriented substantially perpendicularly to the base piles and connect them together, and inclinedly arranged bars which connect the base pile to a central mounting for receiving the pylon of a wind power installation. The connecting body is preferably such that its connecting tubes involve corresponding angles so that they can be connected in butting relationship to the connecting tubes of the base pile and the bars in order to be connected thereto preferably by means of orbital welding.

Preferably that connecting body is formed from pre-assembled tube portions. Those tube portions can be for example welded together and are at corresponding angles relative to each other so that the bars and the base piles can be connected together at suitable angles relative to each other. Such a connecting body is a simple possible way of connecting the bars and the base piles together at the correct angles and spacings relative to each other, in particular by welding, more particularly by means of orbital welding. The connecting body which is of substantially smaller dimensions than the bars, the support structure or the base piles, can be pre-assembled. Because of the smaller dimensions, that pre-assembly operation is simple and the appropriate angles between the tube portions can be set in known fashion. When connecting the bars, the support structure and the base piles together only the connecting tubes of the bars and base piles then have to be fitted together in butting relationship with the connecting body and there is no need to provide any further special angle measurements. That simplifies production of the base structure and the costs are reduced.

Another development of the invention provides that each tube portion is equipped with tie elements which act parallel to its center line and which are provided for spanning over at least one node point in the connecting region of two component parts of the base structure. The use of tie elements in the region of a node point has the advantage that a respective tube portion according to the invention is drawn in the direction of a node point by means of the be elements which in particular are in the form of tie bars. Welded seams in the compression region are thus exposed to reduced load changes whereby at the same time the fatigue characteristics thereof are advantageously reduced. A plurality of tie bars are used on a tube portion, the tie bars being arranged uniformly on a part-circle diameter near the tube wall of the tube portion. That always ensures an advantageous application of force in the region of the node points. The tie bars can be arranged for example with their head end at a bulkhead in a respective end region of the tube portion. The tie elements which in that case are preferably in the form of tie bars also extend parallel to the center line of a respective bar of the support structure for example as far as in a tube portion of a bar extending at an angle thereto or a base pile.

Embodiments of the invention showing further inventive features are illustrated in the drawing in which:

FIG. 1 shows a view of a base structure,

FIG. 2 shows a view of a portion of a base pile used for anchorage in the seabed and the driving pile guided therein, in section,

FIG. 3 shows a partial view of a portion of one of the base piles and the support structure in section according to a first embodiment,

FIG. 4 shows a further partial view of a portion of one of the base piles and the support structure with a connecting body in section according to a further embodiment,

FIG. 5 shows a detail view of a ring flange with sandwich tube connection, and

FIG. 6 shows a fully sectioned overall view of a base pile with sandwich connections.

Reference 1 denotes a base or foundation structure for a hydraulic structure, in particular for an off-shore wind power installation, which has three vertically extending base piles 2, 3 and 4 and a support structure 5 having a plurality of bars 6, 7, 8 and a central mounting 9 for the pylon of the wind power installation (not shown). The base piles 2, 3, 4 stand on the seabed 10, driving piles 11, 12, 13 fixedly connected thereto projecting out of same for anchorage in the seabed. To ensure secure anchoring the driving piles 11 through 13 have a portion which is driven into the seabed and which approximately corresponds to the depth of water at the installation location. The support structure 5 connects at the same time the upper or free ends of the base piles 2, 3, 4 together above the water line 14 so that forces acting on the base structure 1 or the wind power installation, due to wind and wave loads, are advantageously distributed to all three base piles 2 through 4 and their driving piles 11 through 13. In addition, provided at a predetermined depth of water above the seabed 10 is a second support structure 15 having bars 16, 17, 18, which advantageously fixes the three base piles 2 through 4 relative to each other during movement to the installation location or during the pile driving operation. Both the base piles 2 through 4 and the driving piles 11 through 13 and also the posts or bars 6 through 8 of the support structure 5 are preferably of a cylindrical configuration.

FIG. 2 shows a partial view of one of the base piles 2 through 4 with one of the driving piles 11 through 13 accommodated therein in section and is intended in particular to more clearly show the structure thereof. Each of the base piles 2 through 4 has a wall of a plurality of layers 19, 20, 21 of different materials. Introduced between the inner, preferably metallic layer 19 and the outer metallic layer 20 is an intermediate layer 21 comprising a core material such as for example concrete. In its foot region each base pile 2 through 4 has a guide 22 for the driving pile, that reduces its free cross-section at the inner peripheral surface, whereby the driving piles 11 through 13 are prevented from running out during the pile driving operation. In that arrangement the guide is formed by means of four plates 23, 23′ which are arranged at the inner layer 19 of a base pile and which extend at an angle of 90 degrees relative to each other at the inside of the inner layer in the longitudinal direction and extend radially inwardly. To provide a stable end position for the driving piles 11 through 13 in a respective base pile 2 through 4 provided at the outside of each driving pile 11 through 13 at a predetermined spacing beneath the upper and is an annular abutment 24 which comes to lie on the upper ends of the plates 23, 23′ of the guide 22 so that portions of the two piles 2 through 4 and 11 through 13 provide relative to each other an overlap region 25 of a predetermined length. That abutment 24 can also be omitted. Provided at the underside of each base pile 2 through 4 there is also a bottom ring 26 having a seal for sealing off the guide gap relative to the driving pile. That seal can also be omitted depending on the respective use. It is not required for the invention. Each driving pile 11 through 13 has a delimited driving pile head 27 delimited by a bulkhead 28 which is arranged at a spacing from its upper end, that approximately corresponds to double the length of the overlap region 25, closing off the free internal cross-section thereof. Both the driving pile head 27 above the bulkhead 28 and also the gap 29 between the outside of the driving pile 11 through 13 and the inside of the base pile 2 through 4 as well as the part of the base pile above the overlap region 25 are filled with a hardening filling material 30. To improve the tensile strength of the filling material 30, a reinforcement 31 of for example bars is arranged at least portion-wise on the inside of the driving pile wall. Each driving pile 11 through 13 also has beneath the bulkhead 28 at least one opening 32 in its pile wall for advantageous air venting during the operation of driving the pile into the seabed 10.

FIG. 3 shows a partial view of one of the base piles 2 through 4 and the support structure 5 having a bar 6 and the central mounting 9 in section and is intended in particular to more clearly show the structure thereof. Each of the base piles 2 through 4 has a wall comprising a plurality of layers 19, 20, 21 of different material, wherein the wall in particular has a metallic inner layer 19 and a metallic outer layer 20. An intermediate layer 21 of a core material, preferably concrete, is introduced between the inner layer 19 and the outer layer 20. Likewise at least a portion of a bar 6 of the support structure 5 as well as the central mounting 9 of the support structure 5 for the pylon of the wind power installation also has a tube portion 6′, 9′ having an inner layer 117, 118 and an outer layer 119, 120. Here too an intermediate layer 121, 122 of concrete is introduced between the inner layers 117, 118 and the outer layers 119, 120. Preferably each inner layer 19, 117, 118 is in the form of an inner tube and each outer layer 20, 119, 120 is in the form of an outer tube extending at a spacing relative to the inner tube. In this case the inner tube and the outer tube are preferably arranged in mutually coaxial relationship and in particular the gap or intermediate space between the inner tube and the outer tube is completely filled with concrete as the core material.

To improve the strength of the intermediate layer 21, 121, 122, formed from a core material, of each base pile 2 through 4, each bar 6 through 8 and the central mounting 9 of the support structure 5, the core is strengthened with reinforcement. The reinforcement used is in particular concrete reinforcing steel bars 131, 132, 133 which extend in the base piles 2 through 4 and the bars 6 through 8 of the support structure 5 in each case parallel to the respective center lines thereof, whereas annular bars 134, 135 are arranged between the inner layer 118 and the outer layer 120 of the wall of the central mounting 9 as the reinforcement therein.

At its end regions the tube portion 6′ has a bulkhead 123, 124 which is of a plate-shaped configuration and seals off the internal space in the tube portion 6′. The reinforcement of the tube portion 6′ extends beyond a respective bulkhead 123, 124 so that after assembly of the support structure has been effected, concrete can be introduced into the connecting regions, in the form of node points 125, 126, between two component parts of the hydraulic structure such as for example the base piles or the central mounting. In addition provided in the region of the node points 125, 126 are a plurality of tie elements 127, 128, 129, 130 which for example are connected at the head end to a respective bulkhead 123, 124 of a tube portion 6′ of the bar 6 and always respectively project through the inner layer 19, 118 for example of a respective base pile 2 through 4 or the central mounting 9. Each tie element 127 through 130 is force-lockingly connected to the respective inner layer 19, 118 in particular by way of a connecting element such as for example a screw nut. Sleeves can be provided between the inner layer 19, 118 and the outer layer 20, 119 of the respective wall at the through passages for the tie elements 127 through 130 in a respective base pile 2 through 4 and the central tube 9.

That avoids buckling of the wall in the node points 125, 126. In particular it is possible to produce overtensioned connections in the region of the node points 125, 126 by means of the tie elements 127 through 130 whereby the load changes between compression and tensile forces at the weld seams of the base piles 2 through 4 and the central mounting 9 and the bars 6 through 8, extending at a predetermined angle relative thereto, of the support structure 5 are advantageously reduced. Similarly to the support structure 5 the support structure 15 which is provided at a predetermined depth of water between the base piles 2 through 4 can also be equipped with the tube portions according to the invention.

FIG. 4 shows a base pile 2, a bar 6″ and a bar 8″ which are connected together by means of a connecting body 60. Identical and similar components are denoted by the same references or references increased by 100, 200 or 300. In that respect attention is directed to the foregoing description in its entirety.

The base pile 2 has an inner tube which forms the inner layer 19 and which is arranged concentrically in an outer tube forming the outer layer 20. An intermediate layer 21 which here is in the form of concrete is arranged in the intermediate space between the two layers 19, 20. A sandwich connection 50 is arranged at the upper end of the base pile 2. Directed axially upwardly (in relation to FIG. 4) the sandwich connection 50 has a ring flange 52 and a cylindrical connecting tube 51. In this embodiment the base pile has an outside diameter of about 3000 mm. The inner layer 19 and the outer layer 20 are of a wall thickness of 16 mm and the intermediate layer is of a thickness of 85.5 mm. The two bars 6″ and 8″ are formed in a similar way. The bar 6″ has an inner tube which forms the inner layer 317 and which is arranged concentrically in an outer tube forming the outer layer 319. An intermediate layer 321 which here is made from concrete is arranged between the two layers 317, 319. At an axial end of the bar 6″ (on the right-hand side in relation to FIG. 4) the bar 6″ has a sandwich connection 350 connecting the two layers 319, 321. Directed axially towards the right On relation to FIG. 4) the sandwich connection 350 has a ring flange 352 and a connecting tube 351. In this embodiment the bar 6″ is of an outside diameter of about 1100 mm. The thickness of the outer layer 319 is 16 mm and the thickness of the inner layer 317 is also 16 mm. The intermediate layer 321 is of a thickness of 86 mm. The bar 8″ has an outer tube forming the outer layer 219, in which an inner tube forming the inner layer 217 is concentrically arranged. Disposed between the two layers 217, 219 is an intermediate layer 221 of concrete. Arranged in the intermediate layer 221 are concrete reinforcing steel bars 233 for reinforcing the bar 8″. The concrete reinforcing steel bars 233 are connected to a ring flange 252 of the sandwich connection 250 which at an axial end of the bar 8″ interconnects the inner layer 217 and the outer layer 219. The sandwich connection 250 has a connecting tube 251 forming an axial prolongation. In this embodiment the bar 8″ has an outside diameter of about 2000 mm. While the outer layer 219 is of a thickness of 20 mm the inner layer 217 is of a thickness of 25 mm. The intermediate layer is of a thickness of 81.5 mm.

In this embodiment the connecting body 60 comprises three tube portions 61, 62, 63. They are connected together at suitable predetermined angles so that the base pile 2 and the two bars 6″ and 8″ can advantageously be connected together. In this embodiment the tube portions 61, 62, 63 are connected together with the connecting tubes 51, 251, 351 by means of orbital weld seams 55, 255, 355. Naturally it is also possible to use any other connection but orbital welding is highly advantageous as welding apparatuses which are simple to operate can be used for that purpose. Because the bars 6″ and 8″ in the form of sandwich tubes are provided with the sandwich connections 250, 350, preferably at both ends, each having a respective connecting tube 251, 351, they can be connected like conventional tubes to further tubes and the like. Calculation of the connection can be effected in known conventional manner, thereby substantially reducing the complexity involved in construction, maintenance and structural-engineering assessment. Calculation processes which are standardised or allowed for off-shore base structures can be used very substantially without alteration.

The sandwich connection 50 (FIG. 5; the sandwich connections 250, 350 are of a like nature) comprises a short steel ring, referred to as the ring flange 52, which was shaped conically in its cross-section towards one end. At the side which is joined by a weld seam 58 to the connecting tube 51 fixed to the ring flange 52, the thickness of the solid connecting tube 51 is matched by the conical cross-section. The other end of the ring flange 52 receives the reinforcing bars 33 at regular spacings over its entire periphery, the reinforcing bars being passed through a pre-bored opening 71 to the other side of the ring flange 52.

Firstly, preferably upon assembly of a complete base pile 2, 3, 4 (see further Figures), the ring flange 52 is connected to the inner tube 19 of the base pile by a weld seam 55. Thereafter the reinforcing bars 33 are successively introduced into the openings 71 and connected together by means of weld seams 54, 57 on respective sides of the ring flange. Now the outer tube 20 of the base pile is passed over the inner tube 19 and the reinforcing bars 33 and connected by a weld seam 56 to the ring flange 52 which is already fixed to the inner tube 19.

The second ring flange (not shown in the Figures) arranged at the axially opposite end of the bar or the tube is passed to the inner tube 19 and the outer tube 20 over the reinforcing bars 33 which have an overlength portion at the other end. Firstly the two tubes 19, 20 are welded to the second ring flange. Thereafter each reinforcing bar 33 which has not yet been fixed is subjected to a precalculated tensile stress by way of a pulling device (not shown here) and carefully welded to the other end 57.

Then preferably the projecting ends of the reinforcing bars 33 are cut off at the weld locations 57. They are carefully matched to the shape of the fillet channel 72 for weld seams together with the projecting portions by being ground off.

As the next step the internal space between the two tubes 19, 20 is filled with concrete as the intermediate layer 21 until there are no longer any air bubbles in the interior.

The concrete is accordingly preferably kept in a highly fluid condition to achieve good flow and filling properties. The entire base pile 2, 3, 4 is preferably oriented vertically during the filling operation. Alternatively it is possible for the base pile 2, 3, 4 to be mounted at an angle of between 5° and 10° relative to the horizontal on a rotary tube frame structure and caused to slowly rotate along its longitudinal axis in the filling operation. The choice of method depends on the amount of space available and the options afforded in the production premises.

The connecting nodes by means of the sandwich connections 50, 150, 350 and the connecting body 60 are to be calculated and manufactured in conventional and tried-and-tested fashion. That avoids problems in regard to approval of novel and untried construction processes. The assessment criteria used by the certifying institutions for critical components in regard to force-transmitting base foundation structures can still be applied.

FIG. 6 shows a full section of a base pile 402. Identical or similar reference numerals are denoted by reference numerals increased by 400, in that respect reference is directed in its entirety to the foregoing description. The base pile 402 is in the form of a sandwich pile and has an inner tube forming the inner layer 419 and an outer tube forming the outer layer 420. A respective sandwich connection 450 a, 450 b is arranged at each of the axial ends of the inner and outer tubes 419, 420 respectively. The sandwich connection 450 a, 450 b has a ring flange 452 a, 452 b which is shaped conically in cross-section and which connects the inner and outer tubes 419, 420 together. On the other side the ring flange 452 a, 452 b is connected to a tube connection 451 a, 451 b which is in the form of a solid tube. Arranged in the intermediate space between the tubes 419, 420 are reinforcing bars 433 which extend along the longitudinal axis and which extend through openings in the ring flanges 452 a, 452 b, Those reinforcing bars 433 are also connected to the connecting tubes 451 a, 451 b.

The base pile 402 is placed on the seabed 10. Arranged in the interior of the base pile 402 is a driving pile 411 which has a bulkhead 428 in the proximity of its head end, and two air vent openings 432 arranged under the bulkhead 428. The upper region of the driving pile 411 is filled with concrete 430 a. Preferably the concrete 430 a is introduced to a height which approximately corresponds to twice the diameter of the driving pile 411. Concrete 430 b is also introduced in the intermediate space between the driving pile 411 and the base pile 402 in order to form a fixed solid connection between the two piles 402, 411. 

1. A base structure (1) for an off-shore wind power installation having at least a plurality of, in particular three, bases pile (2, 3, 4), and a support structure (5) connecting the upper ends of the base piles (2, 3, 4) for the pylon of the wind power installation, characterised in that each base pile (2, 3, 4) has a wall comprising a plurality of layers (19, 20, 21) of differing material substantially over its entire length, wherein the wall is formed from at least one surface portion having an inner layer (19) and an outer layer (20) and wherein a core material is arranged between the inner layer (19) and the outer layer (20) as an intermediate layer (21).
 2. A base structure as set forth in claim 1 characterised in that the inner layer (19) is in the form of an inner tube and the outer tube (20) is in the form of an outer tube extending at a spacing relative to the inner tube (19).
 3. A base structure as set forth in claim 2 characterised in that the core material is concrete,
 4. A base structure as set forth in claim 2 or claim 3 characterised in that the core material is strengthened with reinforcement (131, 132).
 5. A base structure as set forth in one of the preceding claims characterised in that the base piles (2, 3, 4) are of an axial length such that at an installation location they extend from the seabed (10) to above a surface of water (14).
 6. A base structure as set forth in one of the preceding claims characterised in that the base pile (2, 3, 4) is of a diameter in a range of between 2500 mm and 3500 mm and is preferably about 300 mm, the inner layer (19) and/or the outer layer (10) are of a wall thickness in a range of between 12 mm and 20 mm and the thickness of the core material is preferably in a range of between 60 mm and 120 mm.
 7. A base structure as set forth in one of claims 1 through 6 characterised in that at least one further partial region having a plurality of layers, namely an inner layer (117), an outer layer (119) and an intermediate layer (121) is in the form of at least one tube portion (6′) of a bar (6, 7, 8) of the lattice-like support structure (5) which is composed of a plurality of bars.
 8. A base structure as set forth in claim 7 characterised in that the inner layer (117) is in the form of an inner tube and the outer layer (119) is in the form of an outer tube (119) extending at a spacing relative to the inner tube (117), between which is provided the intermediate layer (121), in particular of concrete.
 9. A base structure as set forth in one of the preceding claims characterised in that arranged at at least one and preferably two axial ends of a base pile (2, 3, 4) and/or a bar (6, 7, 8) is a sandwich connection (50, 250, 350) which connects the inner layer (19, 117) and the outer layer (20, 119) and which in the axial direction forms a prolongation of the base pile (2, 3, 4) and/or the bar (6, 7, 8) in the form of a connecting tube,
 10. A base structure as set forth in claim 9 characterised in that the sandwich connection (50, 250, 350) has a ring flange (52, 252, 352) which is substantially conical in cross-section, wherein the ring flange is connected at one end to the inner layer (19, 117) and the outer layer (20, 119) and at the other end to a connecting tube (51, 251, 351).
 11. A base structure as set forth in claim 10 characterised in that the ring flange (52, 252, 352) has openings (71) for receiving reinforcing bars (33, 233).
 12. A base structure as set forth in one of claims 9 through 11 characterised by at least one connecting body having two or more connecting tubes for connection, in particular welding, to connecting tubes or sandwich connections (50, 250, 350) of a respective base pile (2, 3, 4) and at least one bar (6, 7, 8) of the support structure (5).
 13. A base structure as set forth in claim 12 characterised in that the connecting body is formed from pre-assembled tube portions.
 14. A base structure as set forth in one of claims 7 through 13 characterised in that at at least one of its end regions each tube portion (6′) is provided with a bulkhead (23, 24) which sealingly closes at least its free cross-section.
 15. A base structure as set forth in one of the preceding claims characterised in that each tube portion (6′) has at its end at least one annular connecting flange extending in a plane oriented perpendicularly to the center line of the tube portion (6′). 